1. Field of the Invention
The present invention relates in general to valving methods and devices for controlling the flow of air in a pneumatic tool, and, more particularly, embodiments of the present invention relate to continuous stroke pneumatic tools in which a ball valve is incorporated in their pneumatic circuits.
2. Description of the Prior Art
Typical continuous stroke pneumatic tools include, for example, jackhammers, impact wrenches, scrappers, files, rasps, riveting guns, rotary hammers, chipping hammers, and the like. These tools generally incorporate a pneumatic circuit, which allows air or other pressurized gas to cause the tools to perform their intended function.
Pneumatic circuits in continuous stroke pneumatic tools typically include a valving mechanism to control the flow of pressurized gas (typically air) through the tool. Such pneumatic circuits typically operate so that pressurized gas flows in one direction through the circuit to cause a free floating piston to move within a cylinder in one direction during a power stroke. At about the limit of the piston's movement at the end of the power stroke, the piston strikes a tappet member. The tappet member causes the pneumatic tool to deliver a blow to a bit or other attachment that performs the intended work. Also, at the end of the power stroke, the valve is activated and the flow of gas is reversed. The piston then moves through a return stroke. At the end of the return stroke, the valve is again activated to reverse the flow of gas so that another power stroke may be performed. So long as pressurized gas continues to be supplied to the pneumatic circuit, the pneumatic circuit operates continuously driving the piston between return and power strokes. Some prior pneumatic tools provide an operator with the option of operating the tool in either a continuous stroke or intermittent stroke mode. Prior valving expedients generally involved the use of machined close tolerance metal parts. Such prior expedients were not without their shortcomings. Those concerned with these matters in this art recognized the need for improvement.
A major shortcoming of typical prior art devices and methods is that the required close tolerances within the metal valves made them expensive to make and maintain, and limited their reliability. The prior valves generally could not self-compensate for wear or blockages, so frequent maintenance and replacement were required. The machined parts occasionally became self magnetized, which interfered with the operation of the valves. The steel that was typically used for the valve components was subject to corrosion. Any dirt, metallic particles, or other debris tended to interfere with the operation of the valves. Even excessive lubricant could cause the valve parts to become sticky and move erratically. Remedying such fouling required disassembly, cleaning, and reassembly of the valves, because the prior valves were generally not self purging. Pneumatic tools must often operate in very harsh weather. Any moisture in the valve components tended to cause the valves to freeze or otherwise malfunction.
Previous standard designs included, for example, shuttle, plate, ball and flapper type valves, and were generally of all-metallic construction. These metallic components often required heat treatment and close-tolerance machining for them to function efficiently. In general, these prior valves were prone to fail due to conditions frequently encountered during use.
Moisture is always present in any compressed air system. The tight tolerances between diameters and faces of prior devices often trapped this moisture, particularly when the tool was idle for a while. This frequently caused the prior valves to stick in one position. Due to the moisture present in compressed air systems, in severe weather conditions or prolonged continuous operation of these types of tools, it was not unusual for the water present to freeze and prevent the tool from functioning.
Sometimes similar metals tend to magnetize themselves as the components rub together, giving erratic operation of the valve. There was a long felt need for a solution to this problem.
Because of the tight dimensions between diameters and faces on standard prior art valves, gaps of only a few thousandths of an inch were required with tolerances in the order of plus or minus one or two thousandth of an inch. These gaps were susceptible to causing malfunctions when any debris was ingested into the tool. This caused the valve to jam or leak air past the surfaces that are not closed.
If too much lubricating oil was administered to the prior tools, the excess oil tended to “glue” close fitting moving parts together, especially at lower temperatures.
Metal to metal contact eventually caused wear on one or more components due to the friction between parts. Eventually the prior parts wore to the point where the tool would not operate efficiently. The same surfaces in the prior valves were in contact with each other all the time, inducing wear at specific locations.
Standard prior valves were normally of metallic materials that required heat treatment to enhance their wear capabilities. These valves often required expensive manufacturing operations, such as grinding, to achieve the tight tolerances that were required.
There are many pneumatic tools in use throughout the world. There was a recognized need for a control valve kit that would allow the end users of these tools to retrofit the tools with new and improved control valves without any machining or other difficult to perform operations. The need was for a retrofit valve kit that could be installed using nothing more than conventional hand tools.
The pneumatic tool industry has long recognized the need for better pneumatic tool control valves. In response to such needs, this industry has made a number of attempts to resolve the problems of reliability, and expense of making and maintaining prior pneumatic control valves.
One such attempt is reflected in Haeseller U.S. Pat. Nos. 1,240,708, and 1,240,709, each of which is hereby incorporated by reference herein as though fully set forth hereat. A valve cage is mounted in a valve cage pocket on the side of the casing of a pneumatic percussive tool. A ball in the valve cage rolls back and forth in a chamber between two ports. The ports are in the side of the chamber, not at its opposed ends. A tight seal would require the ball to move laterally into the side ports. Without a tight seal, the valve would be inefficient or inoperative depending on how much leakage occurs. The ball and valve cage appear to be metallic. Hartman et al. U.S. Pat. No. 5,930,899, which is hereby incorporated by reference herein as though fully set forth hereat, discloses a pneumatic scraping tool wherein valving is accomplished by a ball that moves back and forth in a cylindrical bore. At one end of its travel the ball seats on an o-ring that is generally concentric with the longitudinal axis of the cylindrical bore. There is no o-ring at the other end of the ball's travel.
Still other attempts are reflected in other prior patents, including, for example, Hartman et al. U.S. Pat. No. 5,930,899 (ball valve in which a ball is seated at one end of its travel by contact with an O-ring, but other ports appear to be sealed by metal to metal contact with the moveable ball); Koudelka, U.S. Pat. No. 5,183,121 (spring loaded ball engages a plastic seat); Curington U.S. Pat. No. 4,146,097 (a check valve ball engages a conical seat at one end of its travel, with the ball and seat apparently being metal); Hoffman U.S. Pat. No. 4,466,851 (a ball rolls back and forth between seats with both the ball and the seats apparently being metal); and Nelson et al. U.S. Pat. No. 4,416,338 (what appears to be a metal ball rolls between the ends of a chamber, one end of which includes an O-ring seat for the ball), each of which is hereby incorporated herein by reference as though fully set forth hereat.